The present invention relates to a digital synthesizer, a digital copying machine (hereafter digital copier) as well as to a magnification control unit applicable to an image forming apparatus such as a copying machine, a printer, and a facsimile machine, and more specifically to a digital synthesizer, a digital copier, and a magnification control unit in which a magnification can finely be adjusted by a user so that an image with a desired magnification can be formed without generating a magnification error in the image.
In digital synthesizers having functions as a copying machines or those as a printer, calibration for magnification as a copying machine is performed when shipping after manufacture in such a way that a magnification of a formed image will match to a desired magnification, namely so that there does not occur a magnification error. For instance, the magnification in the main scanning direction is calibrated by changing a clock frequency of a laser diode (LD) for writing data, and magnification in the auxiliary scanning direction is calibrated by changing a reading speed of a scanner in such a way that the magnification error is within 1%. Specifically, considering the fact that a document used in reality expands or shrinks due to a change in the humidity of the atmospheric air, and generally the magnification error is maintained at around 0.5%.
Magnification error when reading a document is around 0.3% in the main scanning direction due to the displacement of a CCD during calibration for magnification or aberration of a lens. The magnification error is around 0.1% in the auxiliary scanning direction due to a change in the tolerance of an outer diameter of a pulley when driving the scanner or the like. When writing a data, a magnification error of around 0.2 to 0.3% is generated in the auxiliary scanning direction due to a tolerance of a carrier roller and a difference in the transfer speed of the paper caused by slipping or the like. A magnification error of around 0.3 to 0.5% is generated according to the configuration of the optical system due to residual aberration of the operating system used for data writing (non-uniformity in fxcex8 correction).
A magnification error also occurs due to shrinkage of in the paper when fixing an image. Shrinkage of the paper is generated because the moisture in the paper gets evaporated when the paper is heated during fixing. When the paper is left for a certain period of time after copying, the paper absorbs moisture from the atmospheric air and expands. The degree of expansion varies depending on the humidity in the atmospheric air or the way the paper is stored (when many papers are piled, those papers that are near a top and a bottom of the pile expand, but those inside the pile do not expand because they do not come in contact with the atmospheric air). Shrinkage of the paper occurs both in the main scanning direction and in the auxiliary scanning direction, and it is of the order of 0.4 to 0.5% in an ordinary paper, and in a case of a second original drawing (a semi-transparent paper such as tracing paper) sometimes the order may increase up to around 0.7 to 0.8%. In addition, shrinkage of a document due to humidity also causes a magnification error.
For the reasons as described above, it is important that the magnification of a digital synthesizer is calibrated accurately.
In the case of magnification calibration in a printer, as the types of documents outputted from a printer mainly comprises characters, there occurs no problems within a magnification error as a copying machine, so that specific calibration for magnification has not been made.
There is know a patent publication relating to the processing for size of an image which is the Japanese Patent Laid-Open Publication No. SHO 60-69957 titled xe2x80x9cLaser Beam Recording Apparatusxe2x80x9d that discloses a technology for changing the pixel density by a value in proportion to a rotational speed of a polygon mirror as a clock frequency in the main scanning direction. There is also known the Japanese Patent Laid-Open Publication No. SHO 60-120658 titled xe2x80x9cMethod of Changing Size of an Image Formed by a Semiconductor Laser Printerxe2x80x9d that discloses a technology for changing the size of the printing characters by simultaneously changing the scanning speed of the light beam along with the amplitude of a laser beam from a semiconductor laser. There is also known the Japanese Patent Laid Open Publication No. SHO 62-161270 titled xe2x80x9cDigital Copying Machinexe2x80x9d that discloses a technology for executing the processing for changing size of an image in the main scanning direction when copying a document with changed size by providing a converting unit for varying a pixel frequency generated by an oscillator, processing the data in an image data processing section, and converting the pixel frequency in the converting unit.
In the prior art as described above, however, the magnification is calibrated before the digital synthesizer is shipped. Therefore, the calibration for magnification does not always satisfy the user""s needs in practical use, and it is difficult to suppress the magnification error generated in association with conditions in practical use. In other words, as shrinkage of the paper depends on humidity, a degree of shrinkage varies according to the season, and in a case of a digital synthesizer having been used for a long period of time, displacement in installation thereof may cause a large magnification error, and calibration for magnification when shipping from a plant is not sufficient in order to preventing generation of a magnification error.
The digital synthesizer in which only a small paper size such as A3 or A4 is used, is used as a printer for outputting character data from a personal computer. However, a digital synthesizer in which a paper with large size of A2 or more can be used is recently often used as a printer for outputting CAD data, so that it is strongly required to reduce the magnification error to around 0.3% or below, and calibration of magnification when shipping from a plant is not sufficient for suppressing a magnification error generated during actual use thereof.
Furthermore, causes for generation of a magnification error when a digital synthesizer is used as a copying machine are different from those when the digital synthesizer is used as a printer, therefore, there is the problem that calibration for only one of the two applications (i.e. the copying and the printing) is insufficient. The cause of generation of the magnification error when a digital synthesizer is used as a copying machine is mainly the error in reading with a scanner, an error in forming an image, or a slip error in transporting a paper. However, when a digital synthesizer is used as a printer the cause of generation of the magnification error is mainly the error in forming an image and a slip error in transporting a paper.
Not only in a case of a digital synthesizer, but also in a case of an image forming apparatus like a digital copier, calibration for magnification does not always satisfy user""s needs in practical use, and it has been disadvantageously difficult to suppress a magnification error generated depending on conditions in practical use.
It is an object of the present invention to make it possible to obtain an image having a small magnification error by enabling fine adjustment of a magnification by a user thereof so that an image with a desired magnification can be obtained without any magnification error.
It is another object of the present invention to obtain copy output and printer output with a stable magnification and also with high resolution by enabling fine adjustment of a magnification using a different method for a case when a digital synthesizer is used as a copier and for a case where the digital synthesizer is used as a printer respectively so that an image with a desired magnification can be obtained without any magnification error so that there will occur no magnification error in a formed image and an image with a desired magnification can be formed.
It is still another object of the present invention to enable fine adjustment of a magnification with high precision and also to simplify operations for fine adjustment of a magnification in an image forming apparatus such as a digital synthesizer.
The digital synthesizer according to the present invention comprises a mode switching unit for switching between a copy mode processing for reading image information from a document and forming an image according to the read image information and a printer mode processing for receiving arbitrary data from an external information processing device to generate image information for image formation and forming an image according to the generated image information; and a magnification fine adjustment unit for controlling different control objects in the copying mode processing and printer mode processing respectively and finely adjusting a magnification of an image to be formed. Thus, the magnification can finely be adjusted independently in each mode, therefore, a copy output and a printer output having a negligibly small magnification error can be obtained.
In the digital synthesizer according to the present invention comprises a magnification fine adjustment unit for changing in the copy processing mode a frequency of the write reference clock by controlling the write reference clock generating unit to finely adjust a magnification of an image in the main scanning direction, and/or changing a scanning speed for reading an image from the document by controlling the image reading unit to finely adjust a magnification of an image in the auxiliary scanning direction; and further for changing in the printer mode processing a frequency of the write reference clock by controlling the write reference clock generating unit to change a frequency of the write reference clock to finely adjust a magnification of an image in the main scanning direction and/or changing a rotational speed of the polygon mirror by controlling the rotation control unit to finely adjust a magnification of an image in the auxiliary scanning direction. Thus, the magnification can finely be adjusted independently in each operation mode, therefore, a copy output and a printer output having a negligibly small magnification error can be obtained.
The digital copier according to the present invention comprises a write driving control unit for finely adjusting a copying magnification in the scanning direction of a document by controlling the write reference clock generating unit according to a preset copying magnification for fine adjustment, and/or for finely adjusting a copying magnification in the auxiliary scanning direction of a document by changing a rotational speed of the polygon mirror and a frequency of the write reference clock by controlling the rpm control unit and write reference clock generating unit. Thus, a copying magnification in the main scanning direction as well as in the auxiliary scanning direction can finely be adjusted with high precision and high resolution under stable conditions.
In the magnification control unit according to the present invention, a user can select either the processing for changing a rotational speed of a polygon mirror and a write reference clock frequency at a constant state regardless of a copying magnification or the processing for changing a rotational speed of a polygon mirror and a write reference clock frequency by each 1/M step (M: Copying magnification). Therefore, a user can realize operations for size change convenient for a user, and a user can easily obtain a copy output with a small magnification error desired by the user.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.